1. Field of the Invention
This invention relates to compounds which are acrylate esters of dihaloneopentyl glycol phosphates. The compounds of this invention are reactive flame retardants for acrylic polymeric compositions.
2. Description of the Prior Art
During the past several years, a large number of flame retardants have been developed for use with an almost equally large number of flammable materials. Cellulosic materials such as paper and wood and polymeric materials such as polyolefins, polyurethane, and polystyrene are just two examples of materials for which flame retardants have been developed. For any class of flammable materials, such as synthetic type polymers, those skilled in the art have long been aware that some flame retardant additives are more effective in polymers and polymeric compositions than other flame retardant additives. This is because the efficacy of any flame retardant in polymers or polymeric compositions is measured not only by the flame retardant capability of the additive but also by the ability of the additive to improve or modify, or at least not to detract from, other physical or mechanical properties of the polymer or polymeric composition. The mere fact, therefore, that most flame retardants contain halogen and phosphorus atoms does not assure that any given halogenated or phosphorus-containing compound will impart usable flame retarding characteristics to all or even to any polymeric system.
The prior art has specifically recognized the problems of finding suitable flame retardants for various resins in view of the fact that polymer systems differ substantially in both flammability characteristics and physical properties and there is no predictability whatsoever from one system to another. Thus in the Norris et al paper entitled "Toxicological and Environmental Factors Involved in the Selection of Decabromodiphenyl Oxide as a Fire Retardant Chemical", Applied Polymer Symposium No. 22, 195-219 (1973), the authors state: "A growing recognition of the huge annual toll taken by fire is resulting in more stringent flammability requirements for synthetic polymers in a variety of applications. Because of economic constraints and the need to produce flame resistant polymers without total replacement of existing manufacturing processes, increased flame resistance is generally achieved by incorporation of a fire retardant chemical in the finished product. This chemical is usually based on bromine, chlorine, phosphorus, or nitrogen and may either be chemically reacted or physically blended into the product. Since polymer systems differ markedly in both flammability characteristics and physical properties, selection of a suitable flame retardant depends on a variety of factors that severely limits the number of acceptable materials."
The resultant disadvantages in the utilization of various prior art materials as flame retardants, in general, for plastic compositions include, without limitation, factors such as thermal migration, heat instability, light instability, non-biodegradability, toxicity, discoloration, the large amounts employed in order to be effective, and the unpredictable end results obtained when using the same material in different plastics (note, for example, in Modern Plastics Encyclopedia, Vol. 49, No. 10A, October, 1972, page 650, wherein octabromobiphenyl is suitable for use in polyolefins as a flame retardant thereof, but is not shown for use (or functionally equivalent) as such for the other 27 compositions listed such as ABS; polycarbonates, polystyrene, acrylics and polyurethanes). Thus, it can be seen that the field of flame retardancy is highly sophisticated and consequently requires substantial research effort to achieve a particular desired end result.
In conjunction with the foregoing discussion, the prior art in general suggests the use of halogen-containing materials as "potential" or "possible" flame retardants for plastic materials. However, the prior art also recognizes that any material must be adjudged on a case by case basis because of the unpredictable results of the end product when any additive is incorporated therein. For example, with reference to the use of a halogenated fire retardant in U.S. Pat. No. 3,658,634 attention is directed to the fact that the patentee specifically points out the disadvantages in the use of a halogen-containing fire retardant. In Column 1, lines 14-17, the patentee states: "Therefore, if it is possible to impart fire-retardancy to the thermoplastic polymers without deteriorating the useful properties of the thermoplastic polymers, they can be widely used in the field of inertia, construction and electric industries." In Column 1, lines 26-32 the patentee states: "--the compounds containing chlorine or bromine atoms to be used as fire-retardant agents, are generally sublimated and therefore, the fire retardant agents are sublimated and lost in the process for producing fire-retardant polymers or in afterfinishing processes; accordingly, deteriorations of fire-retardancy or difficulties in use tend to occur more often than not."
In column 1, lines 29-44 the patentee states: "--the compounds containing chlorine or bromine atoms to be used as fire-retardant agents are unstable in most cases when exposed to ultraviolet rays." In Column 1, lines 59-64 the patentee states: "However, as a matter of fact, only very few fire-retardant polymers can be used in actual practice although they are said to have fire-retardant effects, because there are restrictions such as the conditions employed in production attributable to the properties of the fire-retardant agent, or to the properties of the polymers into which they are to be incorporated."
It can be seen, then, from the foregoing discussion and quoted subject matter that the field of flame retardancy is highly sophisticated, unpredictable and requires substantial research to produce an end product (plastic composition) which meets the necessary criteria for utilitarian purposes, particularly under the present day government standards. Thus, there is always a demand for a material which will function as a flame retardant in an acrylic resin and concurrently will not, by incorporation therein, adversely affect the chemical and/or physical and/or mechanical properties of the resultant acrylic resin plastic composition and also have utility.
The complexity of the foregoing situation is illustrated by a brief consideration of the patent literature. In U.S. Pat. No. 2,899,455 there is disclosed a group of aldehyde derivatives of 2,2-dimethyl-1,3-propanediol cyclic hydrogen phosphite which are mentioned as useful as pesticides, plasticizers, solvents, flame proofing agents and intermediates, yet the only elucidated use is that of a pesticide. A later German patent publication, 2,262,336, discloses halogenated neopentylglycol-phosphate esters of organic hydroxy compounds as flame retardants for flexible polyurethane foams and thermoplastic fibers such as poly(ethyleneterphthalate). However, these esters are substantially nonreactive in polymerization reactions of the acrylic acid type and therefore must be classified as additive in nature. A still later patent, U.S. Pat. No. 3,890,409, discloses spirophosphate aromatic ethers which are useful as additive flame retardants.
Balancing all of the foregoing considerations and thereby developing polymeric compositions with good flame retardant characteristics as well as a satisfactory balance of other properties is, consequently a task which has in the past and presently continues to require the exercise of a high degree of inventive skill.